1. Field of the Invention
This invention relates generally to wireless electronic devices, such as a cordless telephone. More particularly, it relates to a method and apparatus for reducing overall AC power requirements of a battery powered cordless device such as a cordless telephone.
2. Background of Related Art
Wireless devices have changed the way many people in the world live. Many homes today have at. least one wireless device, a cordless telephone, a wireless keyboard, a wireless mouse, a digital personal assistant (PDA), a notebook computer, etc. A typical wireless device comprises a base unit which is powered from household AC current, and a remote unit in communication with the base unit and powered by a battery. Communications are generally provided by radio frequency (RF) transmissions between the base and remote units.
Typically, such devices charge the battery of the remote unit while the remote unit is cradled or otherwise mated with the base unit or other xe2x80x9chomexe2x80x9d device. Thus, the battery for a cordless telephone is charged whenever it is placed in its cradle in a base unit. Though a fully charged battery does not require much current to stay fully charged, a drained battery needs a fair amount of current to charge quickly.
Typically, an AC (alternating current) to DC (direct current) adapter is used to provide the necessary power conversion from the AC current of an AC household outlet (e.g., 120 volts, 60 Hz AC) to the base unit of the wireless device. Such an AC to DC adapter is chosen to be sufficiently powerful enough to provide sufficient current to power the base unit and the remote handset during their normal operations, as well as being sufficient to charge the remote handset.
Two general techniques exist for charging a typical rechargeable battery in a wireless device: trickle charge and quick charge. A trickle charge provides a small amount of trickle current (e.g., about 50 mA or less, depending upon the amount of trickle and the battery technology used in the particular application) to the battery to maintain a full charge in an already charged battery, or to slowly build up to a full charge in the rechargeable battery over a period of many hours (e.g., 8 to 15 hours or more). Today, many batteries are capable of charging with a much higher current. Using the higher current, some low batteries are capable of quick charging in, e.g., 60 minutes to 2 hours as opposed to the many, many hours typically required using a trickle charge.
FIG. 5 shows a conventional cordless telephone with an AC to DC adapter sized to sustain quick charge, remote handset operations, and base and remote sniff operations.
In particular, in FIG. 5, a remote handset 500 is cradled in a matching base unit 510. When the remote handset 500 is cradled in the base unit 510, the base unit 510 and remote handset 500 are together powered by an AC to DC adapter 525, which also provides the current to charge the battery 526 of the remote handset 500.
The remote handset 500 and the base unit 510 communicate with one another via the wireless link established between respective RF front ends. Thus, the remote handset 500 continues to periodically sniff the RF front end to detect a transmission from the base unit relating to, e.g., a ring signal or a page signal, and to periodically transmit a request for frequency synchronization information in a xe2x80x9clink verifyxe2x80x9d process. Moreover, the base unit 510 continues to periodically sniff the RF front end to detect activation of the remote handset 500 while it is cradled, e.g., a xe2x80x9cphone onxe2x80x9d activation. Conventionally, this sniffing was not of concern while the remote handset 500 is cradled because it was not causing a drain on the battery 526 in the remote handset 500.
Charging the battery in the remote handset 500 at the same time that normal or other operations in the. remote handset 500 are being performed increases the peak, maximum power requirements for the AC to DC adapter 525. For instance, the RF front end of both the remote handset 500 and base unit 510 are each periodically powered up to sense any incoming signal from the respective matching base unit 510 or remote handset 500, respectively. This periodic sensing is conventionally referred to as xe2x80x9csniffingxe2x80x9d or a xe2x80x9csniffxe2x80x9d operation, and requires a significant amount of current to power the RF receiver to receive any transmitted signal, and to power a codec to digitize the received signal for processing.
In a conventional sniff operation performed by a remote handset 500 of a wireless device such as a cordless telephone, the remote handset 500 powers up its RF receiver to sense if a ring signal or a paging signal is being transmitted by the matching base unit 510. If a signal intended for the particular remote handset 500 is received, the entire RF front end of the remote handset 500 powers up, as do other circuits necessary to respond to the received signal. Similarly, in a conventional sniff operation performed by the base unit 510 of a wireless device such as a cordless telephone, the base unit 510 powers up its RF receiver to sense if any activity has occurred at the remote handset 500, e.g., a xe2x80x9cphone onxe2x80x9d or similar signal. Usually, the base unit 510 is always sniffing (i.e., no sleep or low power time), meaning that the RF off time on the base may be very, very short or even non-existent.
Conventionally, power use is less of a concern in the base unit 510 because it typically receives its power directly from an AC outlet. However, sniff operations performed by the remote handset 500 and base unit 510 add to the size of the power budget of the overall wireless device.
To accommodate the increased size of the power budget due to the sniff operations of the remote handset 500 and/or the base unit 510, an AC to DC adapter 525 is conventionally selected to be of sufficient size capable of providing sufficient current for the worst case situation, e.g., the remote handset 500 and base unit 510 both operating, and the battery 526 in the remote handset 500 being low and receiving a quick charge. Thus, the AC to DC adapter 525 must be sufficiently powerful enough to run both the remote handset 500 and base unit 510 operations, as well as quick charge the battery 526 of the remote handset 500. However, generally speaking, the greater the current draw capability of the AC to DC adapter 525, the more costly and bigger the size of the AC to DC adapter 525 is, adding significant cost to the bill of materials for the wireless device.
Thus, there is a need for a method and apparatus for allowing a reduction in the power requirements of a wireless device, to allow a corresponding reduction in the size (and/or cost) of an AC to DC adapter to power and charge the wireless device, and to reduce the heat generation of the AC to DC adapter and associated power circuitry, allowing for smaller circuit boards and/or for smaller enclosures.
In accordance with the principles of the present invention, apparatus to suppress a sniff operation in a wireless device comprises a charge detector module to detect a presence of charge current from a charging unit of the wireless device to a battery of the wireless device. A sniff module has an enabled mode and a disabled mode. The sniff module is placed in the disabled mode when the charge current is detected.
A method of suppressing a sniff operation in a wireless device in accordance with another aspect of the present invention comprises detecting an electrical coupling between the wireless device and a charging unit. When the coupling is detected, a sniff operation in the wireless device is suppressed.
A method of suppressing a sniff operation in a wireless device in accordance with yet another aspect of the present invention comprises detecting a presence of a remote handset in a cradle of a base unit. When the remote handset is detected as present in the cradle, a sniff operation is suppressed in one of the remote handset and the base unit.